Recent dramatic bridge collapses worldwide have drawn a significant attention on the problem of ageing infrastructural network and highlighted the main failure causes of bridge structures, namely: decay of the mechanical properties due to ageing, increase of traffic loads, subsidence of the soil, earthquakes, and more. Road managers have the great need of acquiring the largest possible information regarding the current health state of the transportation networks that are typically dated and huge in terms of number of bridges. Nowadays, this knowledge is gained through planned inspections to be performed on individual bridges. However, in countries where the seismic risk is high, a special attention must be paid to the seismic response of bridges, as they often constitute the most sensitive and strategic structures for the management of post-earthquake emergencies. Visual inspections are still the most used class of tools to assess the health state of structures after an earthquake. Several efforts have been made to carry out surveys and obtain updated databases on the conditions and the seismic performances of bridges; other efforts have been made to develop automatic procedures for the classification of intervention priorities after seismic events, based on rapid analysis and simplified evaluation forms. The use of seismic structural health monitoring (S2HM) systems installed on the structure can be an excellent solution to these problems. S2HM systems allow reducing the uncertainties affecting the assessment of the planned maintenance and allow important economic savings. The present paper proposes a novel methodology for calculating the life cycle costs of road bridges equipped with S2HM systems. Cost analyses are carried out considering seismic scenarios of the same duration as the life span of the structure, generated through Monte Carlo simulations, based on the mean annual rate values obtained by sampling the seismic hazard curves. The procedure allows to quantify the benefits in terms of structural reliability offered by the S2HM system, and provides knowledge on the economic advantages of the use of S2HM that allows avoiding unnecessary traffic closures and interruptions. The cost model allows to investigate the influence of the seismic monitoring systems on life-cycle cost of bridges and to highlight the most sensitive aspects in order to obtain a significant economic return, such as site seismic hazard and lifetime.
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